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Digestive System
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Digestive SystemGastro-Intestinal System
Continuous tube about 30 feet long from mouth to anus
Smooth muscle in wall- responsible for motility- pushes materials from one end to
another
Functions of Gastro-Intestinal System
Ingest food
Transport food
Digest food into smaller usable components- mechanical & chemical
Absorb necessary nutrients into blood stream
Elimination of waste products from body
Overview of GI function
Breakdown- digestion of macromolecular food stuffs
Controlled absorption of small molecular nutrients
Secretion and absorption of water/ions/ enzymes cofactors/ breakdown products
Motility of food materials down bowel
Production of vitamins- B vitamins, Vit K
Immune surveillance- massive surface area
Structure of Gastro-Intestinal System
Digestive organs
Oral cavity
Pharynx and Oesophagus
Stomach
Small Intestine- duodenum, jejunum, ileum
Large Intestine- caecum with appendix, ascending, transverse, descending and sigmoid colon
Rectum and Anal Canal
Accessory Digestive organs
Teeth, tongue
Salivary Glands
Peritoneum and Mesenteries, Liver, and Biliary System
Gall Bladder
Pancreas
Are connected to GI tract
Assist GI tract into digestion of food
General Structure of Digestive Tract
Common Characteristics: Hollow tube composed of lumen whose
diameter varies
Surrounded by wall made of 4 principal layers called tunics:
Mucosa- epithelial lining
o Lamina propria of loose connective tissues rich in blood, lymph vessels and smooth muscle cells-
muscularis mucosae
, Submucosa- dense connective tissue with blood and lymph vessels and specialised nerve plexi
o E.g. Meissner plexus
Muscle (Muscularis)- contains smooth muscle cells. Divides into 2 layers :
o Internal (Circular)
o External (Longitudinal) - with specialised nerve plexi (myenteric Auerbach’s plexus)
Serosa (or adventitia)- thin layer of loose connective tissue rich in blood and lymph vessels, adipose and
single squamous epithelium- mesothelium
GI structure mostly conserved throughout length
Oral Cavity
Function- Mastication (manual breakdown)
Component parts- Lips, cheeks, tongue, teeth, soft palate, Floor of mouth (with accessory organs- salivary
glands)
Taste buds- Neuroepithelial cells
- Hairs within these cells are receptors stimulated by saliva base on nerve and taste bud
type- sweet, bitter, sour, salty
Salivary glands
Function- secrete saliva to:
o Begin digestion of starch/ carbs
o Keep mouth moist
o Lubricate food
o Helps prevent tooth decay
o Controlling bacterial flora of mouth
3 major glands- Three types of secretory units:
o Serous- amylase, lysozyme- protein secreting
o Mucous- sialomucins – mucin secreting
o Mixed- serous secretion and sialomucins
Histology- Oesophagus
Oesophagus- muscular tube (~25 cm long in adult) that transports food and fluid from
pharynx through thorax and diaphragm to stomach
Lumen usually collapsed except when swallowing food/ liquid
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